Replace plans with pushplans

This branch can be combined with issue #10 either on top of #10 or in lieue of #10.

This branch completely replaces the plans tag with pushplans and is not backwards-compatible (unknown tags will result in KeyErrors in various places). A script is provided in pushplans in the last commit that may be used to rename plans/plans-cleanup to pushplans/pushplans-cleanup in the database.